INDOT’s Highway Traffic Noise Policy is the department’s interpretation of the Federal Highway Administration’s (FHWA) Procedures for Abatement of Highway Traffic Noise and Construction Noise. The INDOT Highway Traffic Noise Policy was approved by the Federal Highway Administration and went into effect on October 15, 1997. The Noise Abatement Criteria (NAC) established by INDOT’s policy is presented in Table 1.

Step 1.	Identify noise-sensitive land uses (receivers) in project area. The Accelerate 465 project team in 2004, the first year of design work, using aerial photos and field reviews, identified the noise-sensitive land uses along the corridor, including residences, apartment and condominium complexes, churches, schools, public building, motels, and parks.
Step 2.	Determine existing noise levels. Short-term, 20 minute Leq(h) noise measurements were taken at twenty-one (21) locations along the corridor in April 2004. One long-term, 48 hour, Leq(h) noise measurement was performed in the backyard of a residence abutting the northbound lanes of I-465 along Hardin Boulevard. Traffic was counted and classified. The traffic data was entered into FHWA’s Traffic Noise Model (TNM® 2.5) to determine the applicability of the model to the specific location allowing for adjustment of variables within the model. Using the data collected in the field along with existing peak hour traffic volumes, existing peak hour Leq(h) noise levels were developed.
Step 3.	Model future design hour noise levels. The FHWA Traffic Noise Model, V2.5 TNM® was used to model future Leq(h) levels for the year 2026 along the entire project study area. The model is a 3-D model which uses coordinates developed from the highway plans to define the proposed roadway improvements, surrounding terrain, potential noise barriers/berms, and the location of noise receivers. Traffic data, hourly volume, number of trucks and operating speed which yield the worst hourly traffic noise impact on a regular basis for the design year were entered into the model. The following parameters were used in TNM® to calculate an hourly Leq(h) at a specific receiver location: Distance between roadway and receiver Relative elevations between roadway and receiver Hourly traffic volumes for light-duty (two axles, four tires), medium-duty (two axles, six tires), and heavy-duty (three or more axles) vehicles Vehicle speed Roadway grade Topographic features, including retaining walls and berms Noise source height of the vehicles Proposed noise barriers
Step 4.	Identify traffic noise impacts. The results of the TNM® modeling were compared to the NAC, Table 1 to determine which noise receivers would be exposed to design hour noise levels that approach or exceed the NAC. Given the volume of automobiles and trucks on the I-465 corridor, the majority of noise receivers adjacent to the roadway presently are and will continue to experience a noise impact.
Step 5.	Identify noise abatement. TNM® is also used to design noise mitigation and determine which noise mitigation measures meet INDOT’s definition of feasible and reasonable. INDOT has defined feasible as being able to reduce the noise level at a receiver by 5dBA. INDOT has established a number of criteria for reasonable mitigation, with the primary point being that based on a noise barrier costing $20.00 per square foot to build, the cost per residence receiving a minimum of a 5dBA reduction should range between $20,000 and $30,000 per residence.
Step 6.	Consideration construction noise. Construction noise is often considered to be short term. On a project of this magnitude, construction noise will be intermittent along the corridor for a number of years. Wherever possible, it is hoped that the approved traffic barriers will be constructed early in the construction process. The actual scheduling of this mitigation cannot be established until final construction sequencing is determined.
Step 7.	Coordinate with local government officials. One goal of the noise study is to inform government officials of future noise levels in the vacant parcels of land along the corridor. Once the study is published, noise mitigation for properties developed after the study will be the responsibility of the developer, not the local government or INDOT.
Step 8.	Inform the public. Public meetings will be held to inform the public of proposed noise mitigation and to provide an opportunity for public comment.
In Summary:	FHWA’s TNM® is used to model the noise levels and design the barriers. Mitigation must provide 5dBA of reduction – meets definition of “feasible”. The cost of the barrier is based up $20.00 per square foot. The total cost of the barrier is divided by the number of residences, not modeled receivers that receive a 5dBA reduction in noise level. The cost per residence must be between $20,000 and $30,000 to meet one of INDOT’s definitions of “reasonable”. Based upon the definition for reasonable, a series of 100 foot wide lots that would need a 15 foot tall barrier would cost $30,000/residence and would be considered reasonable. A group of lots 130 feet wide would cost $39,000 per residence and would not be considered reasonable.
Q3. What can the public expect? The Accelerate 465 team will host three (3) public meetings, one for the northern, one for the central and one for the southern segments of the project corridor. These meetings will be open to the public and will be published three (3) weeks in advance on the project website at www.accelerate465.in.gov and in the Indianapolis Recorder, the Hendricks County Flyer and the Indianapolis Star’s classified sections. The affected homeowners will receive a letter from the project team, defining process and inviting their participation in the noise barrier discussions. The decision to place or not place a noise wall from the recommended noise mitigation evaluation will be a majority decision by the affected homeowners. Final decisions about specific noise abatement will be made after public input has been received and design re-engineering has been addressed. Interested stakeholders that contact the Accelerate 465 team will receive follow-up to questions and/or comments forwarded. Glossary Recognizing the technical requirements of noise mitigation, the following glossary of terms is provided.
A-weighted: The human ear has a non-linear sensitivity to the numerous frequencies that make up noise. Electronic filters are used to define the relative loudness of the different frequencies. The “A” weighting scale is the National and International approved electronic filters or weighting scale used in environmental studies because it resembles the non-linearity of human hearing. dBA: The decibel (dB) is the unit of measurement for noise.  The decibel scale audible to humans spans from zero to approximately 140 dB.  When A-weighting is applied to the noise level, the unit becomes, dBA. Leq(h): Equivalent sound pressure level (Leq), is the equivalent steady-state sound level having the same A-weighted sound energy as that contained in the time-varying sound over the same time period. The time period used for traffic noise is one hour. The abbreviation then becomes Leq(h). Receivers: Residences, apartments, churches, schools, motels, and parks.